1. Field of the Invention
The present invention relates to an inkjet printer head actuator in which a chamber plate has chamber walls defining ink chambers and having a cross-sectional area at its portion coupled to a vibrating plate, larger than the cross-sectional area at its portion opposite to the vibrating plate, thereby achieving an increase in the bonding strength of the chamber plate resulting in an improvement in the performance and ink jetting efficiency of the printer head. The present invention also relates to a method for fabricating such an inkjet printer head actuator.
2. Description of the Prior Art
As well known, an inkjet printer head is a part of an inkjet printer for jetting or firing ink in the form of droplets using an actuator such as a piezoelectric element.
Generally, drop-on-demand (DOD) type printer heads are most widely used for inkjet printers. Such DOD type printer heads are configured to jet or fire droplets of a recording solution onto paper under atmospheric pressure on demand. Use of such DOD type printer heads has increased in that they require no electric charge or deflection of droplets of a recording solution and in that easy printing is achieved, as compared to printer heads of earlier types.
Typical jetting systems of such DOD type printer heads include a heating type jetting system using a resistor and a vibration type jetting system using a piezoelectric element.
The heating type jetting system is also known as a thermal bubble jet type jetting system. Referring to FIG. 1, a typical configuration of such a heating type jetting system is illustrated. As shown in FIG. 1, this heating type jetting system includes a chamber a1 for containing a recording solution therein, and a nozzle a2 provided at the top portion of the chamber al in such a fashion that it is open to a recording sheet (for example, paper). Opposite to the nozzle a2, a resistor a3 is provided at the bottom portion of the chamber a1.
When voltage of a certain level from a voltage source not shown is applied to the resistor a3, the recording solution contained in the chamber a1 is vaporized while being heated by the resistor a3, thereby creating a bubble. Expansion of this bubble creates a pressure forcing a certain amount of the recording solution to be pushed out from the chamber a1 through the nozzle a2. Thus, jetting of the recording solution onto the recording sheet is achieved.
However, such a heating type jetting system involves a problem in that the chemical ingredients of the recording solution itself may vary due to the heat generated from the resistor a3. Such a chemical variation may result in a plugging-up of the nozzle a2. Furthermore, there is a drawback in that the resistor a3 is reduced in its use life span due to repetitive voltage application thereto.
On the other hand, the vibration type jetting system is also known as a piezo transducer type jetting system. Referring to FIG. 2, a typical configuration of such a vibration type jetting system is illustrated. As shown in FIG. 2, this vibration type jetting system includes a chamber b1 for containing a recording solution therein, a nozzle b2 provided at the top portion of the chamber b1 in such a fashion that it is open to a recording sheet (for example, paper), and a piezoelectric element b3 provided at the bottom portion of the chamber b1 opposite to the nozzle b2.
The vibration type jetting system is different from the heating type jetting system in that a recording solution is jetted using the piezoelectric element b3 having a compact structure, in place of the resistor a3 used in the heating type jetting system.
When voltage of a certain level is applied to the piezoelectric element b3, a deformation in the piezoelectric element b3 occurs, thereby resulting in an instantaneous volume variation in the chamber b1. As a result, the recording solution is forced out of the chamber b1 through the nozzle b2. Thus, the recording solution is jetted onto the recording sheet.
Recently, such a vibration type jetting system using a piezoelectric element has been widely used because it can prevent a chemical variation of the recording solution, thereby achieving a more stable jetting of the recording solution, as compared to the heating type jetting system.
Referring to FIG. 3, a conventional inkjet printer head is illustrated which is configured to use the above mentioned vibration type jetting system. In FIG. 3, the reference numeral 1 denotes a nozzle plate formed with nozzles for jetting droplets of ink. The reference numeral 2 is a channel plate 2 formed over the nozzle plate 1.
A chamber plate 3 is layered over the channel plate 2. The chamber plate 3 has vertical through holes open at both ends thereof and adapted to define chambers 3a. A vibrating plate 4 is layered over the chamber plate 3 to cover the chambers 3a. Piezoelectric elements 5 are attached to the upper surface of the vibrating plate 4 at regions corresponding to the chambers 3a, respectively.
Generally, the formation of the chamber plate 3 is achieved by forming a green sheet using a ceramic material in accordance with a screen printing process, forming chambers 3a at the green sheet in accordance with a punching process, and then sintering the punched green sheet.
In the chamber plate 3 fabricated in the above mentioned manner, there are a plurality of uniformly spaced chambers 3a arranged in a matrix array. These chambers 3a have substantially vertical side walls.
Each of the chambers 3a is closed at the bottom thereof by the channel plate 2 and at the top thereof by the vibrating plate 4. The piezoelectric elements 5 attached to the vibrating plate 4 are arranged at regions corresponding to the chambers 3a, respectively.
In the above mentioned structure, each chamber 3a has the same cross-sectional area at the bottom and top thereof. In other words, each side wall of each chamber 3a has the same thickness at its upper and lower ends. Due to such a structure, the vibrating plate 4 exhibits an insufficient bending strain when the piezoelectric elements 5 are strained. As a result, an insufficient ink jetting force is generated. For this reason, the above mentioned structure has a drawback in that it is impossible to achieve a high printing efficiency.
Referring to FIG. 4, another conventional inkjet printer head is illustrated which is configured to use the above mentioned vibration type jetting system. This printer head includes a nozzle plate 10, and a channel plate 20 layered over the nozzle plate 10, as in the case of FIG. 3. A chamber plate 30 having chambers 31 is formed over the channel plate 20 in accordance with an electro-forming process. A vibrating plate 40 is layered over the chamber plate 30 to cover the chambers 31. Piezoelectric elements 50 are attached to the upper surface of the vibrating plate 40 at regions corresponding to the chambers 31, respectively.
In this structure, each chamber 31 formed at the chamber plate 30 has a cross-sectional area increasing gradually as it extends downwardly from the top thereof to the bottom thereof. In other words, each side wall of each chamber 31 has a thickness decreasing gradually as it extends downwardly from its upper end to its lower end.
Due to such a structure, the bending strain of the vibrating plate 40 generated when the piezoelectric elements 5 are strained is smaller than that in the case of FIG. 3. This is because the cross-sectional area of the chamber 31 at the top thereof near the vibrating plate 40 is smaller than that in the case of FIG. 3. As a result, an insufficient ink jetting force is generated which is smaller than that in the case of FIG. 3.
In this structure, therefore, the printing efficiency is further degraded. Moreover, this structure has a very small bonding area between the channel plate 20 and chamber plate 30 because each chamber wall of the chamber plate 30 has a reduced thickness at its lower end bonded to the channel plate 20. Such a very small bonding area results in an insufficient bonding force of the chamber plate 30 to the channel plate 20. For this reason, the bonding of the chamber plate 30 to the channel plate 20 may be damaged as the chamber plate 30 is subjected to the repeated bending strain of the vibrating plate 40. Thus, the printer head involves a degradation in durability resulting in a reduction in use life span.
Therefore, an object of the invention is to provide an inkjet printer head actuator having a chamber plate formed with chambers each having a cross-sectional area decreasing gradually as it extends downwardly from the top thereof to the bottom thereof, so as to maximize a bending moment generated at a vibrating plate attached to the top of the chamber plate, thereby increasing the ink jetting force, so that an improvement in printing efficiency is achieved.
Another object of the invention is to provide an inkjet printer head actuator having a chamber plate provided with chamber walls defining chambers, each of the chamber walls having a cross-sectional area increasing gradually as it extends downwardly from its upper end to its lower end, so as to increase the bonding force of the chamber wall at its lower end, thereby keeping a stable operation while achieving an improvement in durability.
In accordance with the present invention, these objects are accomplished by providing an inkjet printer head actuator including: a vibrating plate having a flat plate shape; a chamber plate coupled to the vibrating plate, the chamber plate having chamber walls defining a plurality of uniformly spaced chambers each having a horizontal cross-sectional area decreasing gradually, as it extends one end thereof arranged toward the vibrating plate to the other end thereof arranged away from the vibrating plate, each of the chamber walls having a horizontal cross-sectional area increasing gradually as it extends one end thereof arranged toward the vibrating plate to the other end thereof arranged away from the vibrating plate; and a plurality of drive means attached to a surface of the vibrating plate opposite to the chamber plate at regions corresponding to the chambers, respectively. In this structure, the resistance moment caused by the bonding force of the chamber plate at the chamber wall end arranged away from the vibrating plate is greater than the total moment generated by each of the drive means.